Lighting systems for a pool illuminate the water at night for the safety of swimmers and for aesthetic purposes. The illumination emanates from underwater lights affixed to the wall of the pool. Although the safety of the pool is enhanced in some respects by the underwater lights, the use of electricity to power the underwater lights creates a risk of electrical shock.
Conventional pool lighting systems typically utilize a household 110-volt (V), 60-Hertz (Hz), alternating-current (AC), three-wire, grounded source of power to supply electrical power to the underwater lights. A cord conducts the electrical power to the underwater lights. In particular, a cord having three wires has one end terminated at a metallic electrical panel, which is coupled to the household electrical power and located at a relatively far distance from the pool near the residence. The cord runs from the electrical panel to a metallic (or nonmetallic) junction box located near the pool. The metallic junction box houses the connection point for the cord to another three-wire cord that leads to the underwater light. The another cord runs from the junction box to the underwater lights. The cords typically run underground through conduit that protects the cord from damage.
Two of the three wires are a "hot" wire and a "neutral" wire that conduct the electrical power to the underwater lights. The household source of power impresses a voltage between the hot wire and the neutral wire to cause an electrical current to flow through the hot wire, the underwater lights, and the neutral wire. In simple terms, the hot wire carries the electrical current from the electrical panel to the underwater lights, and the neutral wire provides a path for the electrical current to return to the electrical panel. The voltage drop due to the current flowing in the wires is typically small compared to the 110-V source, thus a sufficient voltage exists at the pool lights to power them.
A "ground fault" occurs when electrical current strays from the hot wire, the neutral wire, or other current-carrying component of the underwater light, to an electrically conductive component. The conductive component becomes energized, thus causing a risk of electrical shock to a person who may come in contact with it.
The risk of electrical shock due to ground faults can be reduced by several measures.
A "ground" wire is a safety feature of the three-wire, grounded electrical system, providing another path for electrical current to return to the electrical panel. The third wire of the cord is the ground wire. Typically, the electrically conductive components of the underwater light, other than those components that are meant to carry electrical current to the underwater light, are connected to the ground wire. For example, a metallic housing or light reflector in the lighting fixture is "grounded," that is, an electrical connection is made from the housing or reflector to the ground wire. By grounding the conductive component, the stray electrical current can return to the electrical panel by way of the return path provided by the ground wire. Thus, the grounded conductive component is de-energized, reducing the risk of electrical shock.
As an extra safety precaution, the conductive component is "bonded," that is, an electrical connection is made to a conductive net encircling the pool. The conductive net is typically the reinforcing steel bar of the concrete pool walls. Thus, the electrical current can dissipate via the earth.
The risk of electrical shock depends primarily upon the integrity of the grounding and bonding of the lighting system. The integrity of the grounding and bonding can be compromised for various reasons: The ground and bond connections may not be made during the installation of the pool lights; the ground and bond connections can deteriorate due to corrosion; and, the ground connections can be damaged, for example, by a person servicing the light, earthquake tremors, construction, lightning, or rodents. To increase safety due to deterioration and damage, multiple grounds and bonds are made to the conductive components. This redundancy, however, increases the installation costs of the pool lights.
Even if the integrity of the grounding and bonding remains intact, the risk of electrical shock can arise from another source. Because the pool light shares the same ground as the utility service and household electrical system, ground faults from household appliances can be conducted through the ground wire and energize the conductive components of the pool light.
Lighting systems are known that utilize an isolation transformer for supplying a 110-V, 60-Hz, three-wire, grounded source of power to the pool light. The isolation transformer is typically housed in a separate independent electrical enclosure. The isolation transformer isolates the hot wire and the neutral wire of the primary from the output wires of the secondary. These systems do not, however, isolate the ground wire. Thus, ground faults can propagate across the transformer.
Lighting systems are known that utilize an isolation transformer for supplying a two-wire, ungrounded source of power to the pool light. The niches used in these two-wire systems, however, are designed to receive lighting fixtures that are powered by both the three-wire, grounded source of power and the two-wire, ungrounded source of power. For safety, such a niche must have connections for grounding and bonding, and the niche must be bonded to the pool net during installation, to guard against the possibility that a three-wire lighting fixture, or a two-wire lighting fixture having conductive components, will be installed in the niche during the life of the niche.
Typically, a metallic bolt fastens the three-wire or two-wire lighting fixture to the niche, and the bolt can be removed to unfasten the lighting fixture for service or replacement. Furthermore, the bolt is one of various bonding connections that provide an electrically conductive path from the conductive components of the lighting fixture and the niche to the pool net.
Accordingly, not much labor cost is saved in the installation of pool lighting systems when a two-wire, ungrounded source of power is used to power the lighting fixture because of the requirement for grounding connections and bonding connections.
A need therefore exists for a lighting system, which uses a two-wire lighting fixture supplied by a two-wire, ungrounded source of power, that is easier to install than conventional lighting systems without compromising the safety of the lighting system.
Not only safety features but also aesthetic features of the lighting system are important to purchasers of underwater lighting systems.
Conventional pool lighting fixtures employ a single lamp. Thus, to adequately illuminate the underwater area, multiple pool lights are typically arranged around the pool walls to obtain wide coverage of illumination. Even with the scattering of lights, areas along the walls, especially in corners, remain dimly lit because the conventional lighting fixtures are highly directional and project the light forward from the pool wall. Thus, it would be desirable to have a pool lighting fixture that could widely disperse the emanating light.
The single lamp used in pool lighting fixtures is typically an incandescent lamp, although halogen lamps are coming into use. A halogen lamp provides a high-intensity natural white light at about two-thirds the energy consumption of a conventional incandescent lamp at the same illumination. Because of the advantages of the halogen lamp, it would be desirable to employ a halogen lamp in the pool lighting fixture. It is further desireable to use a low-voltage lamp to reduce the risk of shock. Typically, the low voltage is supplied by a transformer. Because of the low voltage, the isolation transformer needs to be located near the lamp to reduce the voltage drop across the wires conducting power to the lamp. Thus, it is not desirable to use low-voltage lamps in pool lights when the isolation transformer is in an electrical panel that is far away from the pool.
Another desirable aesthetic feature of a lighting system is to adjust the intensity of the illumination emanated by the lights. Lighting systems are known that use manually operated (MO) dimmer switches for varying the intensity of the lights. MO dimmer switches are installed on the power line leading to the light, and typically have a rotatable knob that adjusts the intensity of the lights. The combination of a MO dimmer switch and an electronic transformer operates satisfactorily when the connected load is close to the power rating of the electronic transformer. The combination may fail to operate, however, when the load is much lower than the maximum power rating of the electronic transformer.
Lighting systems are also known that use inexpensive two-wire, remote-controlled (RC) dimmer switches, such as, a line of X10 dimmer switches available from Home Automation Systems, Inc.
In one application, a hand-held remote unit is operated by the user, and, in response, the remote unit transmits a radio-frequency (RF) signal of 121 kilohertz to a control unit. The control unit, in response to the RF signal, adjusts the intensity of the light. The RC dimmer switch in this application, however, is specified to be used only with incandescent lamps, because the RC dimmer switch relies upon the conduction path through the incandescent bulb filament for communication. Accordingly, these inexpensive, two-wire RC dimmer switches are not suitable for other types of lamps that interrupt the conduction path.
In another application, a hand-held remote unit is operated by the user, and, in response, the remote unit transmits a radio-frequency (RF) signal to a transceiver unit. The transceiver unit is plugged into a household power outlet within the communication range of the remote unit. The transceiver unit receives the RF signal from the remote unit, and, in response to the RF signal and a zero crossing of the AC signal on the power lines, transmits a dimming control signal over the power lines. The control unit synchronizes its reception of the dimming control signal based on the zero crossing and, in response to the received dimming control signal, adjusts the intensity of the light.
The communication between the transceiver unit and control unit is dependent upon the timing derived from the zero crossing of the AC signal. Nonlinear loads that generate noise on the power line, however, can interfere with the timing of the reception of the dimming control signal. An example of a nonlinear load is a load that has switching occurring in it, such as, electronic transformer model no. CV 10/75-12 available from B plus L Technologies, Ltd.
Furthermore, the noise generated by a nonlinear load can interfere with the dimming control signal. Conventional techniques to reduce the interference are to install isolation devices or noise reducing devices that filter out the noise. These techniques, however, are relatively expensive, requiring the purchase and installation of the devices.
Thus, these inexpensive, two-wire RC dimmer switches are suitable for use in applications where the connected load is linear, but are not suitable for applications where the connected load is nonlinear, such as, halogen lamps powered by an electronic isolation transformer.
A need therefore exists for an underwater lighting system that is easier to install, has improved illumination characteristics, and can employ MO switches and inexpensive RC dimmer switches, without compromising safety.